The invention relates to a beater mill in the grinding chamber of which there rotates a beater rotor which is fitted on its circumference with beater tools and is surrounded by a cylindrical grinding surface adjoined by a coaxial centrifugal classifier. Such beater mills, also referred to as classifier mills, are known in numerous variations having the common feature that the grinding chamber and classifying chamber are mutually separated by a partition, with the oversize particles classified out in the classifying chamber by purposely influencing the classifying air flow being recirculated once again into the grinding chamber.
German Patent 2,444,657, for example, describes such a classifier mill, in which there is arranged between the grinding chamber and classifying chamber a stationary separating disk which forms with the cylindrical grinding surface an annular gap through which the mixture of ground material and air enters the classifying chamber. A spiral flow which produces the classifying effect is imparted there to the flow of ground material by adjustable guide vanes. The oversize particles classified out in this way is recirculated into the grinding chamber through openings that are provided in the separating disk.
German Patent 3,203,324 discloses a classifier mill which is simpler than this and in which only one solid circular disk, which can be adjusted in the axial direction and whose outer rim terminates in the radial direction in front of the beater plates of the beater rotor, is arranged in the region of the housing end wall on the outlet side. The large annular gap created in this way between the disk rim and the housing wall is intended to effect the recirculation into the grinding zone of the oversize particles leaving the grinding surface, it being the case that in the gap which is formed by said circular disk and the housing end wall on the outlet side, the width of which can be adjusted by axial displacement of the circular disk, the fine particles flow off to the central outlet nozzle, and this is additionally supported by stationary guide vanes.
However, as German Patent 1,507,466 shows, the partition between the grinding chamber and classifying chamber can also consist of a circular disk which rotates in common with the beater rotor and whose outer rim forms with the grinding surface an annular gap whose width can be adjusted in order purposely to influence the flow relationships in the classifying chamber.
As may be seen from German Patent 2,122,856, the partition between the grinding chamber and classifying chamber can also be formed by the rotor disk itself, which carries the beater plates and is consequently provided with openings for recirculating into the grinding zone of the oversize particles precipitated in the classifying chamber. The classifying effect is produced there by stationary guide vanes which cooperate with rotating classifier vanes.
It is therefore a common feature of all known classifier mills to recirculate once again into the grinding zone the oversize classified out in the classifying chamber, and this requires quite complicated structural measures, as the cited prior art demonstrates.